DESCRIPTION: (Adapted from the application) The specific aims of the Gnotobiotic Core are 1. to provide germ-free or gnotobiotic rodents and conventional controls to center members as first priority, but to also provide these unique resources to investigators around the world; 2. to establish new genetic stocks and strains of rodents in an axenic, gnotobiotic or conventional status as required by research projects; 3. to provide technical assistance and isolators to maintain axenic and gnotobiotic rodent models; 4. to provide technical assistance to maintain control animals free of disease and inoculated with various gut microbiotas;5. to provide specific pathogen free conditions for maintaining production of a variety of genetically engineered rodents.